RUBBER COMPOUNDS FOR USE IN PRODUCING VEHICLE TIRES

Abstract

The invention provides diene rubber-silica compounds comprising a diene rubber matrix having dispersed therein a silica filler, wherein said silica filler is surface-modified by covalent attachment of a cationic moiety which forms a cation- interaction with the diene rubber matrix. In particular, it provides such compounds in which the diene rubber is styrene-butadiene rubber. Such compounds can be vulcanized and are suitable for producing vehicle tire components, such as tire treads.

Claims

1-15. (canceled)

16. A diene rubber-silica compound comprising: a diene rubber matrix having dispersed therein a silica filler, the silica filler having a surface-modified by covalent attachment of a cationic moiety which forms a cation- interaction with the diene rubber matrix.

17. The diene rubber-silica compound of claim 16, wherein the diene rubber comprises styrene-butadiene rubber, or a blend of styrene-butadiene rubber with a butadiene rubber.

18. The diene rubber-silica compound of claim 16, wherein the cation- interaction is formed between the cationic moiety and a carbon-carbon double bond and/or phenyl ring present in the diene rubber matrix.

19. The diene rubber-silica compound of claim 16 further comprising a substantial absence of any other covalent interactions between the silica filler and the diene rubber matrix.

20. The diene rubber-silica compound of claim 16, wherein the cationic moiety comprises an organic cationic moiety.

21. The diene rubber-silica compound of claim 19, wherein the organic cationic moiety comprises at a cationic group chosen from a quaternary ammonium, a tertiary sulfonium, a quaternary phosphonium, a protonated or alkylated heterocyclic group, a diazonium ion, a guanidinium ion and combinations thereof.

22. The diene rubber-silica compound of claim 16, wherein the cationic moiety attaches to the silica filler via a linking group which forms a covalent bond to the silica filler and a covalent bond to the cationic moiety.

23. The diene rubber-silica compound of claim 22, wherein the linking group is represented by: ##STR00011## in which * denotes a point of attachment of the linking group to a surface of the silica filler; ** denotes the point of attachment of the linking group to the cationic moiety; each R is independently selected from OH, C.sub.1-6 alkoxy and C.sub.1-6 alkyl; and Z is an optionally substituted C.sub.1-12 alkylene group which may be interrupted by one or more groups selected from O, SiR.sub.2 (in which each R is independently OH, C.sub.1-6 alkoxy, or C.sub.1-6alkyl), PR, NR, and OP(O)(OR)O (in which R is H or C.sub.1-6alkyl).

24. The diene rubber-silica compound of claim 22, wherein the linking group is represented by: ##STR00012## in which * denotes a point of attachment of the linking group to a surface of the silica filler; ** denotes the point of attachment of the linking group to the cationic moiety; each R is independently selected from OH, C.sub.1-3 alkoxy and C.sub.1-3 alkyl; and Z is an optionally substituted C.sub.1-12 alkylene group which may be interrupted by one or more groups selected from O, SiR.sub.2 (in which each R is independently OH, C.sub.1-6alkoxy, or C.sub.1-6alkyl), PR, NR and OP(O)(OR)O (in which R is H or C.sub.1-3 alkyl).

25. The diene rubber-silica compound of claim 23, wherein the linking group is represented by: ##STR00013## in which * denotes a point of attachment of the linking group to the surface of the silica filler; ** denotes the point of attachment of the linking group to the cationic moiety; each R is as defined in claim 8; m is an integer from 0 to 12; a is an integer from 0 to 6; and b is an integer from 0 to 6.

26. The diene rubber-silica compound of claim 16, wherein the cationic moiety is selected from any of the following groups: ##STR00014## in which * denotes the point of attachment of the cationic moiety to the surface of the silica filler or to a linking group as defined in any one of claims 7 to 9; R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently selected from H, optionally substituted C.sub.1-12 alkyl, optionally substituted C.sub.3-6 cycloalkyl, optionally substituted C.sub.2-12 alkenyl, optionally substituted C.sub.2-12 alkynyl, optionally substituted aryl, and optionally substituted heteroaryl; each R.sup.5 is independently selected from optionally substituted C.sub.1-12 alkyl and optionally substituted C.sub.3-6 cycloalkyl; X.sup. is a counterion chosen from thiocyanate, carbonate, chromate, bicarbonate, bisulfate, hydroxide, nitrate, phosphate, sulfate, sulfite, thiosulfate, and acetate; n is an integer from 0 to 5; p is an integer from 0 to 4; q is an integer from 0 to 3; and r is an integer from 0 to 2.

27. The diene rubber-silica compound of claim 16 further comprising a vulcanizable diene rubber-silica compound.

28. A vulcanized rubber compound formed by cross-linking a diene rubber-silica compound as claimed in claim 27.

29. A vehicle tire, comprising a vehicle tire component made from the diene rubber-silica compound of claim 16.

30. A silica filler comprising a surface modified by covalent attachment of a cationic moiety capable of forming a cation- interaction with a diene rubber.

Description

[0171] The invention is illustrated further by way of the following non-limiting Examples and the accompanying figures, in which:

[0172] FIG. 1Schematic representation of the reaction between silica, a halogen silane and a tertiary amine in one embodiment of the invention.

[0173] FIG. 2FTIR analysis of unmodified and modified silica with N,N-trimethylamine, N,N-dimethylethylamine, and N,N-dimethyloctylamine.

[0174] FIG. 3TGA curves of unmodified and modified silica with N,N-trimethylamine, N,N-dimethylethylamine, and N,N-dimethyloctylamine.

[0175] FIG. 4a) N1s spectra and b) Br3d spectra obtained from the XPS analysis of modified silica.

[0176] FIG. 5a) Cured and b) Uncured Payne effect of the SSBR/silica compounds.

[0177] FIG. 6a) Stress-strain curves and b) Reinforcement index of the SSBR/silica compounds.

[0178] FIG. 7a) Variation of the loss factor (tan ) as a function of temperature and b) maximum tan and tan at 60 C. and 0 C. of the SSBR/silica compounds.

[0179] FIG. 8Stress-strain curves at 100 C. for the SSBR/silica compounds.

EXAMPLES

[0180] Testing Procedures:

[0181] 1. Payne Effect

[0182] Payne effect was measured using a Rubber Process Analyzer, RPA elite (TA instruments) with strain sweeps from 0.1% to 100% for cured samples and for uncured samples, at a frequency of 1.6 Hz and a temperature of 60 C. The cured samples were vulcanized beforehand inside the equipment chamber according to the vulcanization conditions at 160 C.

[0183] 2. Modulus, Tensile Strength and Elongation at Break

[0184] Modulus, tensile strength (Stress at Maximum Strain) and elongation at break were measured using a universal testing machine Zwick Z05 (Zwick, Germany) operated with a crosshead speed of 500 mm/min according to ASTM D412. Modulus (100% (M100)) and 300% (M300)), tensile strength (Ts) and elongation at break (Eb) were calculated according to the calculations in ASTM D412. The reinforcement index was determined as the ratio of M300 to M100.

[0185] 3. Rebound

[0186] Rebound, the resilience of a rubber sample based on the ratio of returned to delivered energy, was measured according to ISO 8307 using a testing machine Zwick 5109 (Zwick, Germany). Percentage rebound was calculated according to ISO 8307.

[0187] 4. Hardness, Shore A

[0188] Shore A hardness was measured according to DIN 53505 using a universal hardness tester (Zwick, Germany).

[0189] 5. Loss and Storage Modulus, and Loss Factor (Tan )

[0190] Dynamic mechanical measurement of the vulcanized samples was carried out using a Gabo-Netzsch Eplexor. Measurements were performed with a frequency of 10 Hz, a dynamic strain of 1% below 0 C. and 3% at room temperature (RT). The change in the strain at RT was investigated due to softening of the rubber at higher temperatures which can generate noise in the measurements.

[0191] 6. Mechanical Properties at High Temperature

[0192] Mechanical properties of the compounds at 100 C. were measured by a universal testing machine Zwick Z010 (Zwick, Germany) operated with a crosshead speed of 500 mm/min and with a limit strain of 330%. The tests were performed in a temperature chamber at 100 C. Measurements of the dynamic properties of the vulcanized compounds before and after cycling the samples in the tensile machine were carried out on a Gabo-Netzsch Eplexor. Measurements were performed with a frequency of 10 Hz, a dynamic strain of 1% below 0 C. and 3% at room temperature (RT). The change in the strain at RT was investigated due to softening of the rubber at higher temperatures which can generate noise in the measurements. The cycling of the samples was performed in a universal testing machine Zwick Z010 (Zwick, Germany) operated with a crosshead speed of 500 mm/min and with a limit strain of 200%. All samples were cycled 5 times at 100 C.

[0193] Preparation of Rubber Compounds:

[0194] Rubber compounds for tire tread applications were prepared using a non-functionalised solution styrene butadiene rubber (SSBR) as the polymer matrix and pre-modified silica as the filler.

[0195] Materials: [0196] Rubber: Non-functionalised SSBR: Buna VSL 3038-2 HM (Arlanxeo, Germany) [0197] Silica: ULTRASIL 7000 GR (Evonik Resource Efficiency GmbH, Germany) [0198] 3-Bromopropyltrimethoxysilane (abcr, Germany) [0199] N,N-Dimethyloctylamine (abcr, Germany) [0200] N,N-Dimethylethylamine (abcr, Germany) [0201] N,N-Trimethylamine (Sigma Aldrich, the Netherlands) [0202] Sodium thiocyanate (Sigma Aldrich, the Netherlands) [0203] TDAE (Hansen & Rosenthal, Germany) [0204] Zinc oxide (Millipore Sigma, Germany) [0205] Stearic Acid (Millipore Sigma, Germany) [0206] Sulfur (Caldic B.V., the Netherlands) [0207] N-Tertiary butyl benzothiazyl sulphonamide (TBBS) (Caldic B.V., the Netherlands) [0208] Hexadecyltrimethoxysilane (Sigma Aldrich, the Netherlands) [0209] Bis(3-triethoxysilylpropyl)disulfide (TESPD): Si266@ (Evonik Resource Efficiency GmbH, Germany).

[0210] Silica Modification:

[0211] Chemical modification of the silica (ULTRASIL 7000 GR) was performed by reaction with a halogen silane (3-bromopropyltrimethoxysilane) and a tertiary amine in a two-step reaction. Three different tertiary amines were studied: N,N-dimethyloctylamine, N,N-dimethylethylamine, and N,N-trimethylamine. FIG. 1 is a schematic of the reaction in which the tertiary amine is N,N-trimethylamine.

[0212] Step 1: Preparation of Modified Silica:

[0213] Silica (ULTRASIL 7000 GR), 3-bromopropyltrimethoxysilane and the tertiary amine were reacted to form the modified silica. The amount of 3-bromopropyltrimethoxysilane was 15% of the mass of the silica. The molar ratio between the 3-bromopropyltrimethoxysilane and the different amines was established at 1:5. The reaction was performed for 24 hours at 55 C. using toluene as the solvent.

[0214] Step 2: Elimination of the Bromine Formed in Step 1:

[0215] Sodium thiocyanate was used to eliminate the bromine present in the modified silica. The reaction between the modified silica and sodium thiocyanate was carried out for 24 hours at 80 C. using water as the solvent.

[0216] The resulting modified silica was analysed by Fourier Transform Infrared Spectroscopy (FTIR) using the DRIFTS (diffuse reflectance infrared Fourier transform spectrometry) cell. Chemical modification of the silica was confirmed for all samples by the presence of a band at a 2965 cm.sup.1 (corresponding to the symmetric and asymmetric stretching of CH.sub.2 groups) and a band at 1480 cm.sup.1 (corresponding to CH.sub.3 groups) (see FIG. 2).

[0217] The yield of the reactions was measured by Thermogravimetric Analysis (TGA) using a TA 550 device from TA Instruments operating under a nitrogen and air atmosphere with a heating rate of 20 C./min from room temperature to 800 C. The obtained yields were 13% for the reaction with N,N-dimethyloctylamine, 1.5% for the reaction with N,N-dimethylethylamine and 2% for the reaction with N,N-trimethylamine. TGA curves of the unmodified and modified silica produced using the different tertiary amines are shown in FIG. 3.

[0218] In order to confirm that bromine was not present in the modified silica, X-Ray photoelectron spectroscopy (XPS) was performed using a Quantera SXM (scanning XPS microprobe) from Physical Electronics. The data analysis was made using the software Compass for XPS control, Multipak v.9.8.0.19 for data reduction. The presence of nitrogen in the samples confirmed the chemical modification of the silica with the tertiary amines (see FIG. 4). As can be seen from the results in Table 1 below, the use of sodium thiocyanate was effective to eliminate the bromine present in the modified silica. The quantity of bromine present in the silica was below 0.04 wt. %.

TABLE-US-00001 TABLE 1 XPs results of the modified silica Element C N O Na Si S Br Survey spectrum 21.01 2.83 50.95 24.49 0.72 Core spectra 20.56 1.94 51.98 0.18 24.67 0.63 0.04

[0219] Preparation of Rubber Compounds According to the Invention:

[0220] Rubber compounds (SSBR/modified silica) in accordance with the invention were prepared in an internal mixer (Brabender Plasticorder 350S, Duisburg, Germany) with a fill factor of 0.7, initial temperature of 100 C. and rotor speed of 50 rpm. Samples were prepared according to the formulation in Table 2 and in accordance with the mixing procedure in Table 3. Each rubber compound was prepared in two different versions, i.e. with and without the addition of a cornpatibilising agent (hexadecyltrimethoxysilane). The addition of the compatibilising agent during the mixing process decreases the filler-filler interaction during compounding.

TABLE-US-00002 TABLE 2 Formulation of rubber compounds in accordance with the invention Ingredients Quantity (phr = per hundred parts rubber) SSBR - Buna VSL 3038-2 HM 100 Modified silica - 80 + amount of modifier calculated by TGA ULTRASIL 7000 GR + modifier TDAE 37.5 ZnO 2.5 Stearic Acid 2.5 Sulfur 1.4 TBBS 2 Hexadecyltrimethoxysilane 2

TABLE-US-00003 TABLE 3 Mixing procedure of the rubber compounds Time [min:s] Action Step 1 pre-heating 100 C. - 50 rpm 0.00 Add rubber, mastication 1.20 Add filler, silane (compatibilising agent) 2.40 Add filler, silane (compatibilising agent), TDAE 4.00 Add filler, zinc oxide, stearic acid 5.00 Increase torque (increase temperature to 130 C.) 10.00 Stop mixing (reaching 140 C.) Step 2 pre-heating 50 C. - 50 rpm 0.00 Add elastomer pre-mix, mastication 1.30 Add all curatives (sulphur, TBBS) 3.00 Stop mixing

[0221] Details of the final rubber compounds according to the invention are set out in Table 4 below.

TABLE-US-00004 TABLE 4 SSBR/modified silica compounds Compound 1a Silica modified with N,N-dimethylethylamine Compound 1b Silica modified with N,N-dimethylethylamine and the addition of hexadecyltrimethoxysilane during mixing Compound 2a Silica modified with N,N-trimethylamine Compound 2b Silica modified with N,N-trimethylamine and the addition of hexadecyltrimethoxysilane during mixing Compound 3a Silica modified with N,N-dimethyloctylamine Compound 3b Silica modified with N,N-dimethyloctylamine and the addition of hexadecyltrimethoxysilane during mixing

[0222] Preparation of Reference Rubber Compounds:

[0223] The results obtained from the SSBR/modified silica rubber compounds were compared to three reference rubber compounds, details of which are shown in Table 5.

TABLE-US-00005 TABLE 5 Reference SSBR/silica compounds Reference 1 SSBR/silica compound in-situ silanized with TESPD Reference 2 SSBR/pre-modified silica with TESPD Reference 3 SSBR/pre-modified silica with TESPD plus addition of the compatibilising agent during the mixing process

[0224] The reference compounds were prepared according to the formulation shown in Table 6 and in accordance with the mixing procedure used for the compounds according to the invention shown in Table 3 (in which the silane is TESPD or the compatibilising agent, as appropriate).

TABLE-US-00006 TABLE 6 Formulation of reference compounds Ingredients Quantity (phr) SSBR - Buna VSL 3038-2 HM 100 Silica - ULTRASIL 7000 GR 80/80 + Si266* calculated by TGA Si266* 6.2 TDAE 37.5 ZnO 2.5 Stearic Acid 2.5 Sulfur 1.4 TBBS 2 Hexadecyltrimethoxysilane 2 *Bis(3-triethoxysilylpropyl)disulfide (TESPD)

[0225] Testing of Rubber Compounds:

[0226] Results for the measured Payne effect are shown in Table 7 and FIG. 5.

TABLE-US-00007 TABLE 7 Payne effect of the SSBR/silica compounds Vulcanised - Payne effect Unvulcanised - Payne effect Compound G, kPa G.sub.100%, kPa G, kPa G.sub.100%, kPa Reference 1 1301.9 450.3 700.6 134.2 Reference 2 1462.3 429.9 541.5 122.9 Reference 3 1117.4 286.6 331.6 104.4 Compound 1a 4155.1 470.2 1292.3 153.0 Compound 1b 2912.7 219.5 513.8 96.3 Compound 2a 869.0 276.1 530.1 113.9 Compound 2b 671.9 215.0 359.0 87.4 Compound 3a 2406.1 207.2 538.9 85.2 Compound 3b 1182.5 172.7 334.7 80.3

[0227] The results show that for the unvulcanised and vulcanised Payne effect the compounds 2b and 3b according to the invention show a lower Payne effect than the reference compounds. This indicates a reduction in the filler network.

[0228] Results for the mechanical properties of the vulcanised compounds are shown in Table 8 and FIG. 6.

TABLE-US-00008 TABLE 8 Mechanical properties of the SSBR/silica compounds Reinforcement index Ts Eb M100 M300 (M300/ Compound (MPa) (%) (MPa) (MPa) M100) Reference 1 11.4 385 2.24 8.04 3.59 Reference 2 12.7 524 1.62 5.83 3.60 Reference 3 13.4 531 1.52 6.14 4.04 Compound 1a 12.6 625 1.76 4.786 2.72 Compound 1b 9.4 642 0.87 2.946 3.38 Compound 2a 7.9 555 1.301 3.611 2.77 Compound 2b 9.4 595 0.90 3.31 3.68 Compound 3a 10.2 627 0.93 3.45 3.71 Compound 3b 8.6 642 0.69 2.74 3.94

[0229] The mechanical properties show that the compounds 2b and 2c have a higher reinforcement index than the Reference 1 and Reference 2 compounds and slightly inferior than the Reference 3 compound. The tensile strength is inferior in all compounds compared to the Reference compounds and the elongation at break is slightly superior. The values for all compounds according to the invention are considered acceptable with respect to the reference compounds.

[0230] The rebound properties of the compounds and hardness are shown in Table 9. The rebound results show that Compound 2a and 2b present higher values than the Reference compounds. With respect to hardness all compounds according to the invention except for Compound 1a showed lower values than the Reference compounds (see Table 9).

TABLE-US-00009 TABLE 9 Rebound and hardness of the SSBR/silica compounds Rebound at Hardness, Compound 60 C. % Shore A Reference 1 39.8 52.4 Reference 2 40.1 58.8 Reference 3 43.0 53.9 Compound 1a 31.1 59.7 Compound 1b 35.2 47.3 Compound 2a 45.7 41.4 Compound 2b 45.8 35.8 Compound 3a 33.7 42.1 Compound 3b 38.0 35.5

[0231] Results of the dynamic mechanical measurement of the vulcanized samples are set out in Table 10 and FIG. 7.

TABLE-US-00010 TABLE 10 Maximum tan and tan at 60 C. and 0 C. of the SSBR/silica compounds Compound tan at 60 C. tan at 0 C. tan maximum Reference 1 0.189 0.409 0.627 Reference 2 0.180 0.482 0.707 Reference 3 0.167 0.553 0.802 Compound 1a 0.197 0.346 0.575 Compound 1b 0.219 0.508 0.789 Compound 2a 0.161 0.549 0.864 Compound 2b 0.168 0.692 1.084 Compound 3a 0.287 0.579 0.822 Compound 3b 0.249 0.669 1.072

[0232] Analysis of the loss factor (tan ) as a function of the temperature of the compounds according to the invention shows that Compound 2b has lower values of tan at 60 C. (indicating better rolling resistance) compared to Reference 1 and Reference 2, but is similar to Reference 3. Compound 2b presents higher values of tan at 0 C. and a higher maximum of tan (indicating better wet grip) than all reference samples. The values for all compounds according to the invention are considered acceptable with respect to the reference compounds.

[0233] The re-connectivity of the new bonds created with the silica modification according to the invention was analysed by studying the mechanical response of the compounds at high temperatures and analysing the change in dynamic properties after submitting the compounds to a cycling (fatigue test). The results are set out in FIG. 8 and Table 11.

TABLE-US-00011 TABLE 11 Mechanical properties of the SSBR/silica compounds at 100 C. Ts.sup.1 M100 M300 Compound (MPa) (MPa) (MPa) Reference 1 5.3 2.7 Reference 2 5.7 2.7 Reference 3 5.9 2.2 Compound 1a 4.3 1.8 4 Compound 1b 2.8 0.9 2.5 Compound 2a 4.1 1.4 3.8 Compound 2b 3.3 1.0 3.0 Compound 3a 3.3 1.0 3.0 Compound 3b 2.5 0.8 2.3 .sup.1Ts values are for the reference compounds only. For the compounds according to the invention the results are for the Stress at 330% (maximum extension in the heating chamber).

[0234] The results of the mechanical properties measured at 100 C. show that the compounds according to the invention present better resistance to high temperature. All the reference samples were broken before reaching the limit strain established for the experiment (330% strain). However, in the case of the compounds according to the invention, the samples did not break during the experiment indicating that the new bonds created with the silica modification are able to re-connect and consequently resist the tests at high temperatures. The tensile strength and the modulus at 100% are inferior in all compounds according to the invention compared to the references.

[0235] Results of the dynamic mechanical measurement of the vulcanized compounds before and after cycling in the tensile machine are set out in Table 12.

TABLE-US-00012 TABLE 12 Maximum tan and tan at 60 C. and 0 C. of the SSBR/silica compounds tan tan tan at at maxi- 60 C. 0 C. mum after after after tan cycling tan cycling tan cycling 5 times 5 times 5 times at at at at maxi- at Compound 60 C. 100 C. 0 C. 100 C. mum 100 C. Reference 3 0.167 0.211 0.553 0.724 0.802 0.907 Compound 2b 0.168 0.191 0.692 0.793 1.084 1.128

[0236] Compound 2b showed smaller changes in its dynamic properties after being submitted to 5 cycles at 100 C. until 200% strain than reference compound 3.

[0237] The invention has been described with reference to exemplary embodiments. Modifications and alterations are considered to form part of the invention to the extent that they are within the scope of the disclosure and appended claims. The scope of the disclosure should be determined with reference to the claims and is considered to include equivalents.